Reformer process with variable heat flux side-fired burner system

ABSTRACT

An apparatus for heating a fluid in a process having a process heat requirement includes a shell, at least one tube having a design temperature inside the shell, a plurality of burners adjacent the inner wall of the shell, and transfer means whereby flue gas flows from a first interior region to a second interior region of the shell. A first portion of the tube is in the first interior region and a second portion of the tube is in the second interior region. The first and second portions of the tube are adapted to contain a flow of the fluid. The burners produce the flue gas in the first interior region and a variable heat flux approximating the process heat requirement and simultaneously maximizing the heat flux to the first portion of the tube while maintaining substantially all of the first portion of the tube at the design temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

This invention relates to processes involving the heating of fluids,such as processes for the production of a gas containing hydrogen andcarbon oxides by steam reforming a hydrocarbon feedstock, and inparticular to an apparatus and method for hydrocarbon reformingprocesses, hydrocarbon cracking processes, and heating of fluids.

Although the invention is discussed within the context of steamreforming of hydrocarbons, the invention is not limited to use with suchprocesses. The steam reforming process is a well known chemical processfor hydrocarbon reforming. A hydrocarbon and steam mixture (amixed-feed) reacts in the presence of a catalyst to form hydrogen,carbon monoxide and carbon dioxide. Since the reforming reaction isstrongly endothermic, heat must be supplied to the reactant mixture,such as by heating the tubes in a furnace or reformer. The amount ofreforming achieved depends on the temperature of the gas leaving thecatalyst; exit temperatures in the range of 700E-900EC are typical forconventional hydrocarbon reforming.

Conventional catalyst steam reformer processes combust fuel to providethe energy required for the reforming reaction. In a reformer of such aconventional process, fuel typically is fired co-current to incomingcold feed gas to achieve a high average heat flux through the tubewall(s) by radiant heat transfer directly from the flame. Downstreamfrom the burner end, both the product gas and the flue gas exit atrelatively high temperatures.

FIG. 1 illustrates a conventional upflow, up-fired cylindrical reformer10 (or furnace) having three burners 12 located therein. Tubes 14 arefilled with catalyst and run the height of the reformer 10. A processfluid mixture enters through the inlet headers 18 and is injected intothe tubes 14. The fluid mixture travels through the catalyst-filledtubes and exits to the outlet headers 16. The fluid mixture within thetubes is heated almost completely by radiant heat transfer from theburners 12 within the reformer. Only one side of the tube sees directradiation from the flame, which results in non-uniform heating aroundthe tube circumference. The flue gas exiting through the stack 15 is ata very high temperature.

To recover the sensible heat from the product syngas, prior arthydrocarbon reforming processes use a tube within a tube (tube-in-tube)arrangement with catalyst in the annuli. The feed absorbs heat from thecombustion side of the furnace through the outside tube wall. Thereformed gas flow is reversed at the end of the catalyst bed and entersthe inner-most passage of the tube. The reformed gas then gives up heatto the counter-current flow of the incoming cold feed.

When the catalyst is fresh, a large fraction of the heat that istransferred through the tube is absorbed by the endothermic reactionsthat take place at high rates. When the catalyst in this region isdeactivated (poisoned), the endothermic reactions occur at a slower rateand absorb a smaller fraction of the heat. As a result, the temperatureof the process gas in this region is elevated and the tendency forcoking/overheating the tube greatly increases.

U.S. Pat. No. 3,230,052 (Lee, et al.) discloses a terraced heatercontaining two rows of vertical catalyst-filled tubes (in a staggeredarrangement). Each longitudinal wall of the furnace is made up of aseries of planar surfaces that form a series of steps. The base of eachstep incorporates a series of troughs that run along the length of thefurnace and incorporate (linear) burners. The burners inject flames intoeach trough to substantially fill each trough. The combustion iscompleted within the trough. The hot flue gases sweep over the inclinedplanar walls above each trough. The objective is to heat the inclinedrefractory wall to a (relatively) uniform temperature attempting toachieve a uniform heat intensity (heat flux) to the tubes in thatsection of the furnace. By altering the firing rate of any set of pairedburners disposed at the same elevation, different zones of tubes can besubjected uniformly to heat intensities suitable for the reaction rateattainable therein. However, no information is provided on how the heatflux to each vertical section should differ and what determines theamount of fuel to be fired within each elevation. The fuel is burned andreleases its heat of combustion at three discrete elevations in thefurnace and the inclined vertical refractory walls are used in anattempt to evenly heat the tubes.

U.S. Pat. No. 3,182,638 (Lee, et al.) discloses a fired heater designthat utilizes the same type of burners as disclosed in U.S. Pat. No.3,230,052. Burners are located only on the floor. The furnace is dividedinto multiple cells using additional refractory faced walls. The objectis to achieve a uniform heat flux to the serpentine tubes in each zone.The magnitude of heat transferred in each cell can be adjusted bycontrolling the fuel flow rate to each cell via trough burners firingalong opposing walls.

U.S. Pat. No. 5,199,961 (Ohsaki, et al.) discloses an apparatus forcatalytic reaction having a lower radiant heat transfer space and anupper space designed to enhance convective heat transfer to the verticaltubular reactor. In a similar manner as described in U.S. Pat. Nos.3,182,638 and 3,230,052, burner assemblies (called linear burners) arelocated along the furnace floor between rows of tubes. These burnersfire upward along the vertical refractory walls. The intent is todistribute the heat to the tubes more evenly along the height of thetube and to attempt to provide approximately equal heat flow to eachtubular reactor. The fuel is burned and releases its heat of combustionat only one elevation in the furnace. This approach does not solve theproblem of how to tailor the heat flux distribution along the height ofthe tubular reactor with the heat flux distribution required by theprocess (to achieve a uniform tube metal temperature over a substantialheight of the reactor and to hold this temperature in close approach tothe tube design limits). The approach described by this patent will tendto overheat the reactor tube wall in the vicinity of the burners.

U.S. Pat. No. 2,751,893 (Permann) discloses a radiant tubular heater anda method of heating. One object is to provide a method of achieving auniform radiant heat flux around the circumference of the heater tube.To achieve this, Permann claims that the tube must be positioned inrelation to a source of radiant heat in a manner to avoid directimpingement on the tube of the most intense part of the initialradiation and to distribute the radiant heat from the same source toopposite sides of the tubes by re-radiation from opposed radiatingwalls. This requires the tubes to be located between two refractorywalls, with the burners located in the first. The tubes are not in theline-of-sight of the burners. A second object of the heater in U.S. Pat.No. 2,751,893 is similar to that of the terraced heater in U.S. Pat. No.3,230,052 in that both attempt to achieve a distribution of radiant heatalong the length of the tubes. Both arrangements require many individualburners at different elevations and positions (along the circumferenceor length and along the height of the furnace).

An article published in the Aug. 14, 1972 issue of The Oil and GasJournal, titled A New Steam-Methane Reformer Gives High CO/H2 Ratio,provides information about a side-fired reformer designed by SelasCorporation of America. Many burners are located in multiple rows inboth sidewalls of the furnace. The reformer tubes are placed in a singlerow. The actual operating practice of the plant applies the same firingrate to each burner and results in a more or less uniform heat fluxalong the height of the tube.

Another article published in the Feb. 1, 1971 issue of The Oil and GasJournal, titled ASRT Heater—A Break from Tradition, provides informationabout the Short Residence Time (SRT) Heater Technology developed byLummus Company. This heater contains a single row of tubes in aserpentine coil arrangement that is fired on both sides with manyburners (process stream flows across furnace). The objective is toachieve a high heat flux to maximize capacity. Recognizing that tubeoperation is limited by maximum tube metal temperature, the goal is toachieve a tube temperature profile that is as uniform as possible alongthe entire tube height. The burners are manifolded to permit control offiring rate separately at the outlet and inlet ends of the coil. Thearticle states that this approach does not reduce the flue gastemperature in the upper part of the furnace, because doing so normallywould result in lower heat absorption in that area. Therefore, thefurnace is fired throughout the height in an attempt to produce auniform heat flux over an entire zone of the furnace and the flue gasexits at a relatively high temperature.

U.S. Pat. No. 4,959,079 (Grotz, et al.) discloses a furnace and processfor reforming of hydrocarbons. The furnace consists of a radiant sectionand a convective section. The steam and hydrocarbon flow down throughthe catalyst-filled tube, first through the convective section and thenthrough the radiant section. Fuel is fired in the radiant section andthe combustion products flow counter-currently with the process gas inthe convective section. To enhance the convective heat transfer in theconvective section the width is reduced (resulting in higher flue gasvelocities) and extended surfaces (fins) are added to the reformer tube.

U.S. Pat. No. 3,172,739 (Koniewiez) discloses an apparatus thatcomprises a natural-draft primary reforming furnace with an integralsteam generator. The reforming furnace is cylindrical with reformingtubes arranged in a radial pattern inside an annulus. The central ductdoes not contain reformer tubes. A secondary burner fires into thecentral duct to provide for additional steam generation capability.Koniewiez does not discuss the problem of ensuring that (for eachvertical slice of the furnace) each tube is heated uniformly around thecircumference and that each tube segment receives the same amount ofheat. Koniewiez also does not discuss the problem of ensuring that theamount of heat (heat flux) supplied to each segment of the tube does notcause the tube to overheat. No examples are given to illustrate that apractical design can be achieved with the primary floor-mounted burners.(The patent does state that additional burners may be positioned in thewall of the furnace and on the outer surface of the central duct.) Therewill be a very high tendency to locally overheat the bottom of thereformer tubes with floor-mounted burners. The outlet segment of thetube will run hot and will limit the firing rate and average heat flux(heating capacity). The remainder of the tube will be poorly utilizedand will operate well below the design temperature. Floor mountedburners will restrict capacity, aggravate tube temperature, and increasetube wall thickness requirements.

U.S. Pat. No. 3,475,135 (Gargominy) discloses a reforming furnace designwith a rectangular enclosure. Vertical reformer tubes are placed in azigzag arrangement between the longitudinal walls of the enclosure. Tworows of burners are located on the longitudinal walls. Process flow isdownward and the flue gas flow is also downward (co-current flow). Thisfurnace also contains a lower section designed to enhance convectiveheat transfer. In the convective section, the tubes are enclosed inchannels to increase the flue gas velocity and the channels are filledwith refractory pellets. This design approach applies side-fired,down-flow reforming with co-current flow (process gas and flue gas exitat bottom of furnace). The modifications to increase the outsideconvective heat transfer coefficient are added to enhance the overallheat transfer at the outlet end of the tube. At this location, thetemperature driving force (difference between the flue gas and outertube skin temperature) is getting smaller. In contrast, when the fluegas exits counter to the incoming process gas, the heat transfer rate(primarily by radiation to inlet end of the bare tubes) is increasedbecause of a larger temperature driving force.

U.S. Pat. No. 3,947,326 (Nakase, et al.) discloses a vertical tube typecracking furnace for ethylene and the like. Many burners are mountedalong the side walls of the furnace to heat either one or two rows ofvertical reaction tubes located between the sidewalls. The objective isto apply a uniform heat flux along the vertical tubes, which is not anoptimal means to maximize thermal efficiency. (Optimizing thermalefficiency is not an objective of this patent, which teaches a methodthat actually results in a poor thermal efficiency.)

U.S. Pat. No. 5,993,193 (Loftus, et al.) discloses a Variable Heat FluxLow Emissions Burner, which is provided with a plurality of fuel gasinlets for enabling manipulation of the flame shape and combustioncharacteristics of the burner based upon variation in the distributionof fuel gas between the various fuel gas inlets. The purpose of this isto vary the pattern of heat flux being produced when the burnerapparatus is in operation. However, this burner is a circular burnerwith intricate design, apparently aimed at achieving a great degree ofpremixing and reduced NOx emissions. More importantly, the heat fluxpattern of this burner is a longitudinal heat flux distribution alongthe flame. This type of burner is not capable of tailoring the heatrelease profile to match the process requirements.

U.S. Pat. No. 5,295,820 (Bilcik, et al.) discloses a linear burner witha line of nozzles individually selected to operate by an electricallyregulated distributor for the food industry. The intent is to have aburner with a wide range of heating power or turndown ratio.

It is desired to have an apparatus and a method for processes involvingthe heating of fluids (e.g., hydrocarbon reforming, cracking, and otherprocesses) which overcome the difficulties, problems, limitations,disadvantages and deficiencies of the prior art to provide better andmore advantageous results.

It is further desired to have a more efficient and economic process andapparatus for heating, reforming, or cracking hydrocarbon fluids orother fluids;

-   -   It is still further desired to have a reforming technology that        will provide a higher thermal efficiency and production rate by        overcoming the limitations inherent in the prior art.

It is still further desired to have a more efficient technology thatalso is applicable to other fired process heating applications, such asethylene cracking furnaces.

It is still further desired to achieve a prescribed variable heat fluxprofile which matches the process heat requirement and maximizes theheat flux to the tubes in the lower (fired) region of a furnace.

It is still further desired to have an apparatus and a method forhydrocarbon reforming processes which has a simplified burner systemlocated in one region (e.g., the lower region) of the furnace thatachieves a prescribed heat flux profile and makes maximum use of thetube(s) in the fired zone.

It also is desired to have an apparatus and method for hydrocarbonreforming processes which will:

-   -   transfer heat from the combustion space into the process at high        rates (high average heat fluxes);    -   achieve high capacity in a compact furnace design with as few        tubes as possible (maximum throughput per tube);    -   prevent the formation of hot spots on the tubes by achieving        heat flux distributions, axial and circumferential, that supply        the maximum amount of heat possible to a local section of the        tube without causing it to overheat;    -   achieve the maximum possible radiant efficiency (minimum        possible fuel consumption);    -   significantly reduce the potential for coking (hydrocarbon        cracking, carbon formation, fouling, plugging) that commonly        occurs near the process inlet end of the reformer tube;    -   avoid exceeding the tube design temperature limits (and avoid        being constrained to operate with less efficient operating        conditions, such as a high steam-to-carbon ratio and low process        effluent temperature);    -   allow for operating flexibility to continue to achieve design        production rates for an extended period of time;    -   reduce catalyst replacement cost by extending operating time for        a charge of catalyst; and    -   simplify the burner system and associated piping, valves and        controls to reduce capital and maintenance costs.

BRIEF SUMMARY OF THE INVENTION

The invention is an apparatus and method for heating, reforming, orcracking hydrocarbon fluids or other fluids. The invention includes theuse of a variable heat flux side-fired burner system for use inprocesses for heating, reforming, or cracking hydrocarbon fluids orother fluids.

A first embodiment of the apparatus includes: an elongated shell havingan inner wall, a first end, and a second end opposite the first end; atleast one elongated reaction chamber having a design temperature; aplurality of burners adjacent the inner wall; and transfer meansadjacent the second end of the shell. The elongated shell has a firstlongitudinal axis, the shell being substantially symmetrical about thefirst longitudinal axis and enclosing a first interior region adjacentthe first end and a second interior region adjacent the second end. Eachof the first and second interior regions are substantially symmetricalabout the first longitudinal axis. The at least one elongated reactionchamber has a second longitudinal axis substantially parallel to thefirst longitudinal axis. The reaction chamber is substantiallysymmetrical about the second longitudinal axis. A first portion of thereaction chamber is disposed in the first interior region of the shell,and a second portion of the reaction chamber is disposed in the secondinterior region of the shell. The first and second portions of thereaction chamber are adapted to contain a flow of the process fluid.Each of the burners is adapted to combust at least one fuel, therebyproducing a flue gas in the first interior region of the shell and avariable heat flux. The variable heat flux substantially approximatesthe process heat requirement and simultaneously maximizes the heat fluxto substantially all of the first portion of the reaction chamber whilemaintaining substantially all of the first portion substantially at thedesign temperature without substantially exceeding the designtemperature. At least a portion of the flow of the flue gas flows fromthe first interior region of the shell to the second interior region ofthe shell via the transfer means.

In a preferred embodiment, the reaction chamber(s), which preferably isa tubular device, is a reformer tube. The tubular device may be areformer radiant tube or a tube-in-tube device.

There are many variations of the first embodiment of the apparatus. Inone variation, at least a portion of the process fluid flows through atleast the first or second portion of the reaction chambercounter-currently with at least a portion of the flow of the flue gas.In another variation, a substantial portion of the reaction chamber issubstantially vertical within the shell. In yet another variation, aflame is radially directed from the burner substantially toward thefirst longitudinal axis of the shell.

In the preferred embodiment, the shell is substantially cylindrical.However, the shell may have other shapes. In one variation, the shellhas a cross-sectional area substantially in the form of an ellipse. Inanother variation, the shell has a cross-sectional area substantially inthe form of a polygon.

Another embodiment of the invention is similar to the first embodimentof the apparatus but includes at least one refractory wall disposed inthe shell adjacent the burner. The refractory wall is substantiallyperpendicular to the inner wall of the shell.

Yet another embodiment of the invention similar to the first embodimentof the apparatus has a particular burner arrangement using a pluralityof elongated burner assemblies adjacent the inner wall. Each of theburner assemblies has a different longitudinal axis substantiallyparallel to the first and second longitudinal axes, a first end, and asecond end opposite the first end. The first end of the burner assemblyis adjacent the first end of the shell and the second end of the burnerassembly is in the first region of the shell. The burner assemblies aresubstantially equally spaced apart peripherally around the inner walland at least two neighboring burner assemblies are substantiallyequidistant from the reaction chamber. Each burner assembly is adaptedto combust at least one fuel, thereby generating a flue gas in the firstinterior region of the shell. In all other respects, this embodiment issubstantially the same as the first embodiment of the apparatus. As inthe first embodiment, the reaction chamber(s), which preferably is atubular device, is a reformer tube. The tubular device may be a reformerradiant tube or a tube-in-tube device.

Yet another embodiment of the invention is similar to the firstembodiment of the apparatus but has a plurality of rays of one or moreelongated reaction chambers (which may be reformer tubes). Each ray issubstantially perpendicular to the inner wall of the shell. The raysdivide the cross-sectional area of the shell into a plurality ofequally-sized sectors having substantially identical shapes. At leastone burner is disposed in each sector. Each of the reaction chambers hasa design temperature and a different longitudinal axis substantiallyparallel to the first longitudinal axis and is substantially symmetricalabout the different longitudinal axis. A first portion of each reactionchamber is disposed in the first interior region of the shell and asecond portion of each of the reaction chambers is disposed in thesecond interior region of the shell. The first and second portions ofthe reaction chambers are adapted to contain a flow of the processfluid. In all other respects, this embodiment is substantially the sameas the first embodiment of the apparatus.

Another aspect of the invention is a method for producing a product froma process for heating, reforming, or cracking hydrocarbon fluids orother fluids. The process may have a heat requirement for heating theprocess fluid.

A first embodiment of the method includes multiple steps. The first stepis to provide an elongated shell having an inner wall, a firstlongitudinal axis, a first end, and a second end opposite the first end.The shell is substantially symmetrical about the first longitudinal axisand encloses a first interior region adjacent the first end and a secondinterior region adjacent the second end. Each of the first and secondinterior regions is substantially symmetrical about the firstlongitudinal axis. The second step is to provide at least one elongatedreaction chamber having a design temperature and a second longitudinalaxis substantially parallel to the first longitudinal axis. The reactionchamber is substantially symmetrical about the second longitudinal axis.A first portion of the reaction chamber is disposed in the firstinterior region of the shell and a second portion of the reactionchamber is disposed in the second interior region of the shell. Thefirst and second portions of the reaction chamber are adapted to containa flow of the process fluid. A third step is to provide a plurality ofburners adjacent the inner wall, each of the burners being adapted tocombust a fuel. The fourth step is to combust at least one fuel in atleast one of the burners, thereby producing a flue gas in the firstregion of the shell and a variable heat flux. The variable heat fluxsubstantially approximates the process heat requirement andsimultaneously maximizes the heat flux to substantially all of the firstportion of the reaction chamber while maintaining substantially all ofthe first portion substantially at the design temperature withoutsubstantially exceeding the design temperature. The fifth step is totransfer at least a portion of a flow of the flue gas from the firstinterior region of the shell to the second interior region of the shell.The sixth step is to feed at least a portion of the process fluid to thereaction chamber, wherein the portion of the process fluid absorbs atleast a portion of the heat flux.

In a preferred embodiment of the method, the reaction chamber(s), whichpreferably is a tubular device, is a reformer tube. The tubular devicemay be a reformer radiant tube or tube-in-tube device.

There are many variations of the first embodiment of the method. In onevariation, at least a portion of the process fluid flows through atleast the first or second portion of the reaction chambercounter-currently with at least a portion of the flow of the flue gas.In another variation, a flame is radially directed from the burnersubstantially toward the first longitudinal axis of the shell.

Another embodiment of the method is similar to the first embodiment ofthe method but includes an additional step. The additional step is towithdraw a stream of the product from the reaction chamber. Yet anotherembodiment of the method is similar to the first embodiment except forthe third step and the use of a particular burner arrangement. In thethird step of this embodiment, a plurality of elongated burnerassemblies are provided adjacent the inner wall. Each of the burnerassemblies has a different longitudinal axis substantially parallel tothe first and second longitudinal axes, a first end, and a second endopposite the first end. The first end of the burner assembly is adjacentthe first end of the shell and the second end of the burner assembly isin the first region of the shell. The burner assemblies aresubstantially equally spaced apart peripherally around said inner walland at least two neighboring burner assemblies are substantiallyequidistant from the reaction chamber. The burner assemblies are adaptedto combust at least one fuel. In all other respects, this embodiment issubstantially the same as the first embodiment of the method. Thereaction chamber in this embodiment may be a reformer tube.

Yet another embodiment of the method is similar to the first embodimentof the method except for the second step. In the second step of thisembodiment, a plurality of rays of one or more elongated reactionchambers are provided. Each ray is substantially perpendicular to theinner wall, and the rays divide the cross-sectional area of the shellinto a plurality of equally-sized sectors having substantially identicalshapes. Each of the reaction chambers has a design temperature and adifferent longitudinal axis substantially parallel to the firstlongitudinal axis. Each of the reaction chambers is substantiallysymmetrical about the different longitudinal axis. A first portion ofthe reaction chamber is disposed in the first interior region of theshell and a second portion of the reaction chamber is disposed in thesecond interior region of the shell. The first and second portions ofthe reaction chamber are adapted to contain a flow of the process fluid.With regard to the fourth step in this embodiment, at least one burneris disposed in each of the sectors. In all other respects, thisembodiment is substantially the same as the first embodiment of themethod.

Yet another aspect of the invention is a variable heat flux side-firedburner system for use in a process for heating, reforming, or crackinghydrocarbon fluids or other fluids, the process having a process heatrequirement for heating a process fluid in at least one reaction chamberhaving a design temperature, a first portion, and a second portion. Theburner system includes a plurality of adjacent burner units adapted tocombust at least one fuel, thereby producing a variable heat flux. Thevariable heat flux substantially approximates the process heatrequirement and simultaneously maximizes the heat flux to substantiallyall of a first portion of the reaction chamber while maintainingsubstantially all of the first portion substantially at the designtemperature without substantially exceeding the design temperature.

There are several variations of the first embodiment of the burnersystem. In one variation, the adjacent burner units are equally spacedapart and each burner unit combusts the at least one fuel at a differentfiring rate. In another variation, the adjacent burner units arevariably spaced apart and each burner unit combusts the at least onefuel at a substantially identical firing rate. In yet another variation,the adjacent burner units are variably spaced apart and each burner unitcombusts the at least one fuel at a different firing rate. In still yetanother variation, at least one burner unit combusts at least one firstfuel or a fuel mixture containing said first fuel and at least one otherburner unit combusts at least one second fuel or a fuel mixturecontaining said second fuel.

Another embodiment of the burner system is similar to the firstembodiment but also includes a common fuel supply, a common air supply,means for regulating a flow of fuel to each burner unit from the commonfuel supply, and means for regulating a flow of air to each burner unitfrom the common air supply.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention will be described by way of example with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic partial cross-sectional elevation of a prior artreformer;

FIG. 2 is a schematic cross-sectional plan view of the prior artreformer shown in FIG. 1;

FIG. 3 is a schematic partial cross-sectional elevation of the apparatusfor one embodiment of the invention;

FIG. 4 is a schematic cross-sectional plan view of the embodiment of theinvention shown in FIG. 3;

FIG. 5 is a schematic partial cross-sectional elevation of the apparatusfor another embodiment of the invention;

FIG. 6 is a schematic cross-sectional plan view of the embodiment of theinvention shown in FIG. 5;

FIG. 7 is a schematic partial cross-sectional evaluation of theapparatus for another embodiment of the invention;

FIGS. 8, 9 and 10 are schematic cross-sectional plan views of theembodiment of the invention shown in FIG. 7;

FIG. 11 is a graph illustrating an S curve for a typical reformer tubeat design conditions;

FIG. 12 is a graph illustrating the maximum heat flux as a function ofprocess gas temperature;

FIG. 13 is a graph illustrating an optimal firing profile for a variableheat flux burner;

FIG. 14 is a graph illustrating tube heat flux distribution resultingfrom the optimal firing profile;

FIG. 15 is a graph illustrating the temperature distribution for fluegas, tube skin and process gas corresponding to the optimal firingprofile;

FIG. 16 is a schematic diagram of a side view of one embodiment of avariable heat flux burner system including deflectors;

FIG. 17 is a schematic diagram of a front view of the variable heat fluxburner system (of FIG. 16) without the deflectors;

FIG. 18 is a schematic diagram illustrating a variable heat flux burnersystem including a fuel supply distributor for distributing fuel to theburner units;

FIG. 19 is a schematic diagram of a burner tip;

FIG. 20 is a schematic diagram of another burner tip;

FIG. 21 is a schematic diagram illustrating a burner arrangementgenerating a flame having a sheet-like shape to provide a variable heatrelease pattern;

FIG. 22 is a schematic diagram illustrating another burner arrangementgenerating multiple flames to provide a variable heat release pattern;and

FIG. 23 is a schematic diagram illustrating another burner arrangementgenerating multiple flames to provide a variable heat release pattern.

DETAILED DESCRIPTION OF THE INVENTION

The invention is an apparatus and a method for an advanced reformingprocess using a variable heat flux side-fired burner system. Theinvention is not, however, limited to reforming applications. Personsskilled in the art will recognize that the apparatus, method, and burnersystem may be used in many other fired process heating applications,including but not limited to fluid heating and hydrocarbon cracking(e.g., ethylene cracking).

The process uses a reformer (or furnace) that has the followingfeatures: an integrated side-fired burner that produces a prescribedvariable heat flux profile tailored to the process to achieve maximumcapacity and maximum thermal efficiency, and avoids coking at the tubeinlet; firing on both sides of tubes in the lower region (adjacent thetube outlet) to maximize the heat flux without overheating the tube (inthe fired region) and no firing in the upper region, with optimalradiant heat transfer between the process gas and the flue gas due tocounter-current flow; radially-directed firing and process tubealignment for optimal heat transfer around the tube circumference;unique burner system design to provide continuous and linear firing withvariable heat flux; and optional refractory walls that extend radiallyfrom the inner wall of the furnace toward the center of the furnace,wherein the burners fire on both sides of each refractory wall, whichhelps to achieve the optimal heat flux distribution to the tubes.

FIGS. 3 and 4 show a schematic of the reformer 20 of the presentinvention (without optional refractory walls), and FIGS. 5 and 6 show aschematic of the reformer with optional refractory walls 22. Referringto FIGS. 3-6, the reformer 20 of the present invention includes arefractory lined shell 24. In a preferred embodiment, the shell iscylindrical. However, persons skilled in the art will recognize that thecross-sectional area of the shell may have alternate shapes, such as apolygon (e.g., a triangle, square, rectangle, pentagon, hexagon,octagon, etc.), an ellipse, or other shapes. Multiple variable heat fluxburners 26 are located adjacent the inner wall of the shell 24 near thelower end of the shell. In a preferred embodiment, the burners arerecessed in the refractory lining of the inner wall. As shown in FIGS. 3and 5, envelopes of the flames 28 are sheet-like. At the upper end ofthe shell (opposite the burner end), there are one or more openings 30that allow the flue gas (containing combustion products) to flow fromthe shell. Conventional reformer tubes 32 containing catalyst arepositioned within the interior of the shell to utilize high intensiveradiant heat directly from the flames of the burners. In the preferredembodiment, the burners are equally spaced apart peripherally around theinner wall of the reformer, with neighboring burners being equidistantfrom one or more reformer tubes positioned in a vertical plane midwaybetween the neighboring burners.

Persons skilled in the art will recognize that the burners may bearranged differently in other embodiments, one of which is illustratedin FIGS. 7-10. As shown in FIG. 7, one or more burners 26 may bearranged within each of the (four) sectors of the reformer 20 to achievethe desired variable heat flux profile to the tubes 32 in the lowerregion of the reformer. As shown in FIGS. 8, 9 and 10, multiple burnersare fired in each pie-shaped sector (Aquadrant@) at different elevationson both sides of tubes arranged in a given ray of tubes. FIG. 8 showsthree burners firing within each quadrant and within a given slice ofthe reformer as a means of increasing the heat release rate within thatslice of the furnace. FIG. 9 shows two burners firing within eachquadrant and within a given slice of the reformer as a means ofincreasing the heat release rate within that slice of the furnace. AndFIG. 10 shows one burner firing within each quadrant and within a givenslice of the reformer as a means of increasing the heat release ratewithin that slice of the furnace. The burners in FIGS. 7-10 are arrangedas shown to ensure that the amount of heat that a given segment of eachtube receives is approximately equal. (Persons skilled in the art willrecognize that many burner arrangements other than that shown in FIGS.7-10 are feasible. For example, one or more additional burners could beadded in each sector at each elevation in FIGS. 8-10.)

In the preferred embodiment, the tubes 32 are arranged in four sectorsof the reformer 20 and one variable heat flux burner 26 is located atthe inner wall in each sector, as shown in FIGS. 4 and 6. (Personsskilled in the art will recognize that the reformer may be evenlydivided into any number of equally-sized sectors with a ray of tubes ineach sector.) Each burner produces a substantially continuous flamealong the height of the burner. The flame front only extends a shortdistance from the burner toward the centerline of the reformer. Heat isradiated directly from the flame and the burner tile to the tubes and isemitted and reflected from the inner wall. Mixed-feed enters the inletheader 34 and is distributed to the upper end of each reformer tube 32.Product synthesis gas exits at the lower end of each reformer tube andis removed from the reformer at the outlet header 36, and the flue gasexits from openings 30 at the top of the reformer.

FIGS. 5 and 6 show a reformer that incorporates four vertical refractorywalls 22, one in each sector. The hot flue gases (containing combustionproducts) flow radially across both sides of each refractory wall, whichis thereby heated and radiates heat to the tubes. The refractory walls22 are perpendicular to the inner wall of the shell 24. These refractorywalls may be made of a composite of conventional refractory materials,such as high temperature fired bricks, or a solid casting of arefractory, such as alumina.

Fuel is fired in the lower region of the reformer 20. The fuel is firedvia the variable heat flux burners 26, which produce a prescribed heatflux profile along the tube length—one that is tailored to the specificrequirements of the process (reforming, or cracking, or other) takingplace inside the tube. This prescribed heat flux profile simultaneouslyaddresses constraints such as design tube metal temperature and coking,and maximizes average heat flux (capacity) and thermal efficiency.

The heat flux profile produced by the variable heat flux burner 26 isdesigned to radiate the maximum amount of heat to each segment of thetube 32 in the fired zone without exceeding the tube design temperaturelimits. The objective is to provide the maximum possible heat fluxthrough each tube segment that is located in the vicinity of the processoutlet. (For reforming applications, the maximum heat flux is tied tothe reforming reaction process that occurs as the gas flows through thetube.) As an intentional result, the tube wall temperature is maintainedat a uniform value over most of the entire fired length of the tube.

For a cylindrical reformer design, each variable heat flux burner 26 islocated along the inner wall of the reformer 20 mid-way between two raysof tubes 32 (as illustrated in FIGS. 4 and 6), and an optionalrefractory wall 22 extends in the radial direction along the center lineof each burner (as illustrated in FIG. 6). The optional refractory wallsare incorporated along the height of the fired region, but not in theunfired region. The refractory walls are used to ensure that the optimalheat flux distribution is attained in the fired region.

In the preferred embodiment, each variable heat flux burner 26 firesfuel substantially continuously over the height of the reformer 20occupied by the burner. The heat release intensity per unit length ofthe burner is very low and varies smoothly along the height of theburner.

The firing rate per burner 26 can be varied for startup and operation atreduced production rates. An objective is to achieve the same relativeheat release profile (% of total heat release versus burner height) overthe burner capacity range. (Persons skilled in the art will recognizethat an adjustable burner could be designed to vary the relative heatrelease profile.) In this way, the variable heat flux profile producedby the burner satisfies all of the constraints (e.g., tube temperature,coking problem) over the turndown range. At turndown conditions, thetube wall temperature will again be similar to design conditions, onlycooler.

For the configurations shown in FIGS. 3 and 5, combustion products flowupward. The combustion products produced by the lower sections of thevariable heat flux burners 26 combine with the combustion productsproduced by the upper sections of the burners and flow upward.

The upper region of the reformer 20 is not fired. The flue gas(containing combustion products) flows counter-currently with theincoming process gas and exits at the top of the reformer.Counter-current flow helps to maximize the heat flux to the tubes in theupper region of the furnace by maximizing the temperature driving force.

This arrangement helps to maximize throughput (capacity) whilesimultaneously achieving maximum possible radiant efficiency. Theimprovement in radiant efficiency at reduced rates will be even betterthan any improvement realized with co-current reforming technology.

The burner and tile design, as well as the design layout of thereforming tubes 32, achieve a uniform heat flux at each elevation in thereformer 20, both around the circumference of individual tubes and fromtube to tube. As a result, the ratio of the peak heat flux to the worsttube (tube with the maximum local heat flux at a given elevation) andthe average heat flux to all the tubes at the same elevation is held asclose to unity as possible. The optional refractory walls 22 furtherensure that this challenging objective is met.

FIG. 11 plots the process duty-process temperature curve, also known asan S curve, for typical reformer tube design conditions (space velocity,catalyst size and shape, end-of-run catalyst activity). This plot isobtained from a steam methane reformer simulation program. At a givendistance from the inlet of the tube, an amount of heat is transferred tothe process gas that causes both the sensible and chemical enthalpy ofthe process gas to increase. The S curve plots the fraction of heatabsorbed (from the inlet to a given point inside the tube) versus theprocess gas temperature at that point.

The reformer tube is designed for a given operating life correspondingwith specified limits on tube wall temperature and process pressure.Once the local conditions inside of the tube are known, it is possibleto calculate the maximum local heat flux that the tube can sustain. FIG.12 plots the maximum heat flux as a function of the process temperaturefor the conditions corresponding to FIG. 11.

From the above discussion, it is clear that limits exist on themagnitude of heat flux to the tube and these limits depend on theprocess temperature and extent of the reforming reaction. Thisinformation is of key importance in specifying the design requirementsof the variable heat flux burner for the side-fired application. Tomaximize the reformer efficiency with downward process flow, it isdesirable to maximize the firing in the bottom region of the reformerand to allow counter-current heat exchange between the combustionproducts and incoming process gas.

FIG. 13 illustrates the shape of the optimal firing profile forreforming natural gas with steam to produce hydrogen. This profile isfor one specified design tube metal temperature and specific fixedprocess conditions. In other words, the reformer tubes are designed forone temperature and the process conditions of temperature and pressureare fixed, as is the capacity (i.e., fixed amounts of natural gas andsteam are fed to the reformer). The amount of fuel fired per unitincrement of reformer height tends to increase from a low value at thebottom of the reformer. The amount of fuel fired to the upper-mostsection of the burner tends to be less than the amount set by tubetemperature constraints (reach target on total firing duty).

FIG. 14 shows the corresponding tube heat flux profile. In the firedregion, the heat flux reaches the maximum heat flux limits as shown inFIG. 12. In the unfired region, the heat fluxes are below these limits.

FIG. 15 plots the corresponding temperature profiles for flue gas, tubewall and process gas. In the fired region, the tube wall temperature isheld at the design limits. With counter-current flow, the differencebetween the flue gas and tube wall temperatures is maximized and thetemperature profiles do not pinch at the flue gas exit.

The advantages of the novel burner and arrangement of the presentinvention include:

-   -   the variable heat flux burner produces the desired heat flux        profile along the tube to maintain relatively constant reformer        tube metal temperature in the fired region;    -   fewer burners, piping, valves and instrumentation are required,        thereby minimizing capital cost for the reformer, or heater, or        ethylene cracker; and    -   the furnace (or reformer) is capable of producing higher        capacity and higher radiant efficiency.

Also, the unique placement of the variable heat flux burner solves thecoking problem that occurs at the tube inlet (in conventional reformers)and extends run time between catalyst changes.

In a typical commercial reformer, such as that illustrated schematicallyin FIG. 1, process gas flow is upward and the reformer 10 is up-firedfrom three burners 12 located near the center of the furnace floor. Thereformer contains tubes in a cylindrical arrangement. TABLE 1 Comparisonof physical configuration Present Reformer Design Prior Art InventionNumber of burners 3 4 Firing direction Upward Side Process flowdirection Upward Downward

In comparing a typical commercial reformer with a reformer according tothe present invention, the following parameters were kept at the samevalues for both reformers for the comparison:

-   -   inside furnace diameter;    -   inside furnace height;    -   reformer tube design temperature and pressure;    -   catalyst activity;    -   catalyst size and shape (single hole);    -   air preheat temperature; and    -   steam-to-carbon (S/C) ratio.

The following benefits of the reformer according to the presentinvention were expected in making this comparison:

30% increase in H₂ production capacity (with same size furnace);

-   -   12% less firing per unit H₂ production;    -   convection section is smaller because of 12% reduction in flue        gas flow;    -   38% less catalyst per unit H₂ production;    -   40% less tube material per unit H₂ capacity; and    -   40% increase in average heat flux based on inside tube surface        area.

Additional work also was done to examine the heat flux distributionswithin this novel reformer which utilizes variable heat flux burners.The results indicate (for a furnace with 4 sectors) that the heat fluxaround the tubes and from tube to tube is expected to be uniform at eachelevation.

FIGS. 16-23 show several arrangements of the variable heat flux burner26 of the present invention. (Persons skilled in the art will recognizethat other burner arrangements are possible.) An important feature ofthe burner used in the preferred embodiment of the present invention isthat it is a relatively long burner, preferably oriented in the verticaldirection on the inner wall of the reformer 20. To be flexible, theburner may be divided into multiple sections, as shown in FIGS. 16-18.But all sections preferably share a common air supply 38 and a commonfuel supply 40. This way, the piping, valves, and controls aresimplified. Each section has a predetermined firing pattern. When joinedtogether, the multi-section burner produces a heat release profile thatoptimally matches for the process conditions.

As shown in FIGS. 16-18, each section has the same way of introducingfuel and air that produces a compact flame, similar to a conventionalwall radiant burner. But it is stressed that FIGS. 16-18, show a singleburner 26 with multiple sections, rather than multiple burners, becauseall sections share a common air supply 38, a common fuel supply 40, anda common burner control system (not shown).

FIG. 16 is a side view of one design of a variable heat flux burner 26used in the present invention. Air 38 enters a conduit 42 at the bottomor top of the burner and air flow to each burner unit or section isregulated by a damper 44. A flame deflector 46 may be associated witheach burner unit or section to shape the flame. FIG. 17 provides a viewof the burner without deflectors as viewed from inside the reformer 20.FIG. 18 provides a view of the burner from outside of the reformer 20showing the supply of fuel 40 to the individual burner units or sectionsvia a distribution system including a manifold 48, piping 50 and controlvalves 52. Different types of burner tips may be used with the burner26. FIG. 19 is a schematic of one such burner tip 54, and FIG. 20 is aschematic of another such burner tip 56.

As indicated, the flame 28 in the preferred embodiment has a sheet-likeshape shown in FIG. 3 and also in FIG. 21. The sheet-like shape may begenerated from a variable heat flux burner 26 such as that illustratedin FIGS. 16-18. However, other burner arrangements and flame shapes,such as those shown in FIGS. 22 and 23, also may be used to generate thevariable heat release pattern in the present invention. For thearrangement illustrated in FIG. 22, the burner units are equally spacedbut each unit is designed to fire at a different firing rate to generatea variable heat release pattern. For the arrangement illustrated in FIG.23, all burner units are designed to fire at the same firing rate andthe spacing between burner units is varied to provide a variable heatrelease pattern. A variable burner unit spacing can also be combinedwith burner units designed to fire at different rates to achieve theprescribed heat flux profile.

Although each burner unit in the preferred embodiment of the inventionburns the same fuel, different fuels may be used in alternateembodiments. For example, selected burner units may be designed to firea liquid fuel (such as naphtha) and other burner units may be designedto burn a gaseous fuel (such as the offgas produced from pressure swingadsorption). It also is feasible for selected burner units to bedesigned to fire a mixture of fuels (such as a mixture of natural gasand offgas from pressure swing adsorption).

Although illustrated and described herein with reference to certainspecific embodiments, the present invention is nevertheless not intendedto be limited to the details shown. Rather, various modifications may bemade in the details within the scope and range of equivalents of theclaims and without departing from the spirit of the invention.

1. An apparatus for heating, reforming, or cracking hydrocarbon fluidsor other fluids in a process having a process heat requirement forheating a process fluid in the process, comprising: an elongated shellhaving an inner wall, a first longitudinal axis, a first end, and asecond end opposite said first end, said shell being substantiallysymmetrical about said first longitudinal axis and enclosing a firstinterior region adjacent the first end and a second interior regionadjacent the second end, each of said first and second interior regionsbeing substantially symmetrical about said first longitudinal axis; atleast one elongated reaction chamber having a design temperature and asecond longitudinal axis substantially parallel to said firstlongitudinal axis, said reaction chamber being substantially symmetricalabout said second longitudinal axis, a first portion of said reactionchamber being disposed in said first interior region of said shell and asecond portion of said reaction chamber being disposed in said secondinterior region of said shell, said first and second portions of saidreaction chamber adapted to contain a flow of said process fluid; aplurality of burners adjacent said inner wall, each of said burnersadapted to combust at least one fuel, thereby producing a flue gas insaid first interior region of said shell and a variable heat fluxsubstantially approximating said process heat requirement andsimultaneously maximizing said heat flux to substantially all of saidfirst portion of said reaction chamber while maintaining substantiallyall of said first portion substantially at said design temperaturewithout substantially exceeding said design temperature; and transfermeans adjacent the second end of said shell, whereby at least a portionof a flow of said flue gas flows from the first interior region of saidshell to the second interior region of said shell.
 2. An apparatus as inclaim 1, wherein at least a portion of said process fluid flows throughat least the first or second portion of said reaction chambercounter-currently with at least a portion of said flow of said flue gas.3. An apparatus as in claim 1, wherein a substantial portion of saidreaction chamber is substantially vertical within said shell.
 4. Anapparatus as in claim 1, wherein said shell is substantiallycylindrical.
 5. An apparatus as in claim 1, wherein said shell has across-sectional area substantially in the form of an ellipse.
 6. Anapparatus as in claim 1, wherein said shell has a cross-sectional areasubstantially in the form of a polygon.
 7. An apparatus as in claim 1,wherein a flame is radially directed from said burner substantiallytoward said first longitudinal axis of said shell.
 8. An apparatus as inclaim 1, further comprising at least one refractory wall disposed insaid shell adjacent said burner, said refractory wall beingsubstantially perpendicular to said inner wall.
 9. An apparatus forheating, reforming, or cracking hydrocarbon fluids or other fluids in aprocess having a process heat requirement for heating a process fluid inthe process, comprising: an elongated shell having an inner wall, afirst longitudinal axis, a first end, and a second end opposite saidfirst end, said shell being substantially symmetrical about said firstlongitudinal axis and enclosing a first interior region adjacent thefirst end and a second interior region adjacent the second end, each ofsaid first and second interior regions being substantially symmetricalabout said first longitudinal axis; at least one elongated reformer tubehaving a design temperature and a second longitudinal axis substantiallyparallel to said first longitudinal axis, said reformer tube beingsubstantially symmetrical about said second longitudinal axis, a firstportion of said reformer tube being disposed in said first interiorregion of said shell and a second portion of said reformer tube beingdisposed in said second interior region of said shell, said first andsecond portions of said reformer tube adapted to contain a flow of saidprocess fluid; a plurality of burners adjacent said inner wall, each ofsaid burners adapted to combust at least one fuel, thereby producing aflue gas in said first interior region of said shell and a variable heatflux substantially approximating said process heat requirement andsimultaneously maximizing said heat flux to substantially all of saidfirst portion of said reformer tube while maintaining substantially allof said first portion substantially at said design temperature withoutsubstantially exceeding said design temperature; and transfer meansadjacent the second end of said shell, whereby at least a portion of aflow of said flue gas flows from the first interior region of said shellto the second interior region of said shell.
 10. An apparatus forheating, reforming, or cracking hydrocarbon fluids or other fluids,comprising: an elongated shell having an inner wall, a firstlongitudinal axis, a first end, and a second end opposite said firstend, said shell being substantially symmetrical about said firstlongitudinal axis and enclosing a first interior region adjacent thefirst end and a second interior region adjacent the second end, each ofsaid first and second interior regions being substantially symmetricalabout said first longitudinal axis; at least one elongated reactionchamber having a second longitudinal axis substantially parallel to saidfirst longitudinal axis, said reaction chamber being substantiallysymmetrical about said second longitudinal axis, a first portion of saidreaction chamber being disposed in said first interior region of saidshell and a second portion of said reaction chamber being disposed insaid second interior region of said shell; a plurality of elongatedburner assemblies adjacent said inner wall, each of said burnerassemblies having a different longitudinal axis substantially parallelto said first and second longitudinal axes, a first end, and a secondend opposite said first end, the first end of said burner assembly beingadjacent the first end of said shell and the second end of said burnerassembly being in said first region of said shell, said burnerassemblies being substantially equally spaced apart peripherally aroundsaid inner wall and at least two neighboring burner assemblies beingsubstantially equidistant from said reaction chamber, each said burnerassembly adapted to combust at least one fuel, thereby generating a fluegas in said first interior region of said shell; and transfer meansadjacent the second end of said shell whereby at least a portion of aflow of said flue gas flows from the first interior region of said shellto the second interior region of said shell.
 11. An apparatus as inclaim 10, wherein said reaction chamber is a reformer tube.
 12. Anapparatus for heating, reforming, or cracking hydrocarbon fluids orother fluids in a process having a process heat requirement for heatinga process fluid in the process, comprising: an elongated shell having aninner wall, a first longitudinal axis, a cross-sectional area, a firstend, and a second end opposite said first end, said shell beingsubstantially symmetrical about said first longitudinal axis andenclosing a first interior region adjacent the first end and a secondinterior region adjacent the second end, each of said first and secondinterior regions being substantially symmetrical about said firstlongitudinal axis; a plurality of rays of one or more elongated reactionchambers, each ray being substantially perpendicular to said inner wall,said rays dividing said cross-sectional area into a plurality ofequally-sized sectors having substantially identical shapes, each ofsaid reaction chambers having a design temperature and a differentlongitudinal axis substantially parallel to said first longitudinalaxis, and being substantially symmetrical about said differentlongitudinal axis, a first portion of each said reaction chamber beingdisposed in said first interior region of said shell and a secondportion of each said reaction chamber being disposed in said secondinterior region of said shell, said first and second portions of saidreaction chamber adapted to contain a flow of said process fluid; aplurality of burners adjacent said inner wall, at least one burner beingdisposed in each said sector and each of said burners adapted to combustat least one fuel, thereby producing a flue gas in said first interiorregion of said shell and a variable heat flux substantiallyapproximating said process heat requirement and simultaneouslymaximizing said heat flux to substantially all of said first portion ofeach reaction chamber while maintaining substantially all of said firstportion substantially at said design temperature without substantiallyexceeding said design temperature; and transfer means adjacent thesecond end of said shell, whereby at least a portion of a flow of saidflue gas flows from the first interior region of said shell to thesecond interior region of said shell.
 13. A method for producing aproduct from a process for heating, reforming, or cracking hydrocarbonfluids or other fluids, the process having a process heat requirementfor heating a process fluid, comprising the steps of: providing anelongated shell having an inner wall, a first longitudinal axis, a firstend, and a second end opposite said first end, said shell beingsubstantially symmetrical about said first longitudinal axis andenclosing a first interior region adjacent the first end and a secondinterior region adjacent the second end, each of said first and secondinterior regions being substantially symmetrical about said firstlongitudinal axis; providing at least one elongated reaction chamberhaving a design temperature and a second longitudinal axis substantiallyparallel to said first longitudinal axis, said reaction chamber beingsubstantially symmetrical about said second longitudinal axis, a firstportion of said reaction chamber being disposed in said first interiorregion of said shell and a second portion of said reaction chamber beingdisposed in said second interior region of said shell, said first andsecond portions of said reaction chamber adapted to contain a flow ofsaid process fluid; providing a plurality of burners adjacent said innerwall, each of said burners adapted to combust at least one fuel;combusting said at least one fuel in at least one of said burners,thereby producing a flue gas in said first region of said shell and avariable heat flux substantially approximating said process heatrequirement and simultaneously maximizing said heat flux tosubstantially all of said first portion of said reaction chamber whilemaintaining substantially all of said first portion substantially atsaid design temperature without substantially exceeding said designtemperature; transferring at least a portion of a flow of said flue gasfrom said first interior region of said shell to said second interiorregion of said shell; and feeding at least a portion of said processfluid to said reaction chamber, wherein said portion of said processfluid absorbs at least a portion of said heat flux.
 14. A method as inclaim 13, comprising the further step of withdrawing a stream of theproduct from said reaction chamber.
 15. A method as in claim 13, whereinat least a portion of said process fluid flows through at least thefirst or second portion of said reaction chamber counter-currently withat least a portion of said flow of said flue gas.
 16. A method as inclaim 13, wherein a flame is radially directed from said burnersubstantially toward said first longitudinal axis of said shell.
 17. Amethod for producing a product from a process for heating, reforming, orcracking hydrocarbon fluids or other fluids, the process having aprocess heat requirement for heating a process fluid, comprising thesteps of: providing an elongated shell having an inner wall, a firstlongitudinal axis, a first end, and a second end opposite said firstend, said shell being substantially symmetrical about said firstlongitudinal axis and having a first interior region adjacent the firstend and a second interior region adjacent the second end, each of saidfirst and second regions being substantially symmetrical about saidfirst longitudinal axis; providing at least one elongated reformer tubehaving a design temperature and a second longitudinal axis substantiallyparallel to said first longitudinal axis, said reformer tube beingsubstantially symmetrical about said second longitudinal axis, a firstportion of said reformer tube being disposed in said first interiorregion of said shell and a second portion of said reformer tube beingdisposed in said second interior region of said shell, said first andsecond portions of said reformer tube adapted to contain a flow of saidprocess fluid; providing a plurality of burners adjacent said innerwall, each of said burners adapted to combust at least one fuel;combusting at least one fuel in at least one of said burners, therebyproducing a flue gas in said first region of said shell and a variableheat flux substantially approximating said process heat requirement andsimultaneously maximizing said heat flux to substantially all of saidfirst portion of said reformer tube while maintaining substantially allof said first portion substantially at said design temperature withoutsubstantially exceeding said design temperature; transferring at least aportion of a flow of said flue gas from said first interior region ofsaid shell to said second interior region of said shell; and feeding atleast a portion of said process fluid to said reformer tube, whereinsaid portion of said process fluid absorbs at least a portion of saidheat flux.
 18. A method for producing a product from a process forheating, reforming, or cracking hydrocarbon fluids or other fluids,comprising the steps of: providing an elongated shell having an innerwall, a first longitudinal axis, a first end, and a second end oppositesaid first end, said shell being substantially symmetrical about saidfirst longitudinal axis and enclosing a first interior region adjacentthe first end and a second interior region adjacent the second end, eachof said first and second interior regions being substantiallysymmetrical about said first longitudinal axis; providing at least oneelongated reaction chamber having a second longitudinal axissubstantially parallel to said first longitudinal axis, said reactionchamber being substantially symmetrical about said second longitudinalaxis, a first portion of said reaction chamber being disposed in saidfirst interior region of said shell and a second portion of saidreaction chamber being disposed in said second interior region of saidshell; providing a plurality of elongated burner assemblies adjacentsaid inner wall, each of said burner assemblies having a differentlongitudinal axis substantially parallel to said first and secondlongitudinal axes, a first end, and a second end opposite said firstend, the first end of said burner assembly being adjacent the first endof said shell and the second end of said burner assembly being in saidfirst region of said shell, said burner assemblies being substantiallyequally spaced apart peripherally around said inner wall and at leasttwo neighboring burner assemblies being substantially equidistant fromsaid reaction chamber, said burner assemblies adapted to combust atleast one fuel; combusting said at least one fuel in at least one ofsaid burner assemblies, thereby producing a combustion heat and a fluegas in said first interior region of said shell; transferring at least aportion of a flow of said flue gas from said first interior region ofsaid shell to said second interior region of said shell; and feeding atleast a portion of a process fluid to said reaction chamber, whereinsaid portion of said process fluid absorbs at least a portion of saidcombustion heat.
 19. A method as in claim 18, wherein said reactionchamber is a reformer tube.
 20. A method for producing a product from aprocess for heating, reforming, or cracking hydrocarbon fluids or otherfluids, the process having a process heat requirement for heating aprocess fluid, comprising the steps of: providing an elongated shellhaving an inner wall, a first longitudinal axis, a cross-sectional area,a first end, and a second end opposite said first end, said shell beingsubstantially symmetrical about said first longitudinal axis andenclosing a first interior region adjacent the first end and a secondinterior region adjacent the second end, each of said first and secondinterior regions being substantially symmetrical about said firstlongitudinal axis; providing a plurality of rays of one or moreelongated reaction chambers, each ray being substantially perpendicularto said inner wall, said rays dividing said cross-sectional area into aplurality of equally-sized sectors having substantially identicalshapes, each of said reaction chambers having a design temperature and adifferent longitudinal axis substantially parallel to said firstlongitudinal axis, and being substantially symmetrical about saiddifferent longitudinal axis, a first portion of each said reactionchamber being disposed in said first interior region of said shell and asecond portion of each said reaction chamber being disposed in saidsecond interior region of said shell, said first and second portions ofsaid reaction chamber adapted to contain a flow of said process fluid;providing a plurality of burners adjacent said inner wall, at least oneburner being disposed in each said sector and each of said burnersadapted to combust at least one fuel; combusting said at least one fuelin at least one of said burners, thereby producing a flue gas in saidfirst interior region of said shell and a variable heat fluxsubstantially approximating said process heat requirement andsimultaneously maximizing said heat flux to substantially all of saidfirst portion of said reaction chamber while maintaining substantiallyall of said first portion substantially at said design temperaturewithout substantially exceeding said design temperature; transferring atleast a portion of a flow of said flue gas from said first interiorregion of said shell to said second interior region of said shell; andfeeding at least a portion of said process fluid to said reactionchamber, wherein said portion of said process fluid absorbs at least aportion of said heat flux.
 21. A variable heat flux side-fired burnersystem for use in a process for heating, reforming, or crackinghydrocarbon fluids or other fluids, the process having a process heatrequirement for heating a process fluid in at least one reaction chamberhaving a design temperature, a first portion, and a second portion,comprising: a plurality of adjacent burner units adapted to combust atleast one fuel, thereby producing a variable heat flux substantiallyapproximating said process heat requirement and simultaneouslymaximizing said heat flux to substantially all of said first portion ofsaid reaction chamber while maintaining substantially all of said firstportion substantially at said design temperature without exceeding saiddesign temperature of said reaction chamber.
 22. A variable heat fluxside-fired burner system as in claim 21, further comprising: a commonfuel supply; a common air supply; means for regulating a flow of fuel toeach burner unit from said common fuel supply; and means for regulatinga flow of air to each burner unit from said common air supply.
 23. Avariable heat flux side-fired burner system as in claim 21, wherein saidadjacent burner units are equally spaced apart and each burner unitcombusts said at least one fuel at a different firing rate.
 24. Avariable heat flux side-fired burner system as in claim 21, wherein saidadjacent burner units are variably spaced apart and each burner unitcombusts said at least one fuel at a substantially identical firingrate.
 25. A variable heat flux side-fired burner system as in claim 21,wherein said adjacent burner units are variably spaced apart and eachburner unit combusts said at least one fuel at a different firing rate.26. A variable heat flux side-fired burner system as in claim 21,wherein at least one burner unit combusts at least one first fuel or afuel mixture containing said first fuel t least one other burner unitcombusts at least one second fuel or a fuel mixture containing saidsecond fuel.